He also served as an Avenger. That’s where I first encountered the character and I liked his time on the team.

I shamefacedly have to confess that I don't remember anything of his time on that team, but then there were long periods when I did not read The Avengers. I was aware that he had been a member, but thanks for clearing up that he was a team player at the time. Also, my unstated reason for focusing on the Invaders and the Defenders was that these were teams that Namor helped found and set up.

Namor's team-related activities go even further. He used to be partnered with Doctor Doom - definitely not a team player - for quite some time, i.e. most of the run of the original Super-Villain Team-Up, and he also belonged to that retconned-in cabal, the Illuminati.